Re: [Qemu-discuss] QCOW2 real hard drive image

[Mike Lovell]

On 08/18/2012 02:03 AM, Jerzy Grzegorek wrote:
> I'd like to create the smallest possible qcow2 (or other format) real 
> hard drive image. It is possible to create it without "dirty" no used 
> sectors in the way like this (with additional options)
>
> qemu-img convert -f raw /dev/sda -O qcow2 disk.qcow2.img

unfortunately, i don't think qemu-img can determine whether or not a 
sector is 'dirty.' i'm guessing by 'dirty' you mean a sector that has 
had data written to it but the file system on top no longer needs the 
data because the file was removed or truncated or similar. determining 
which sector is 'dirty' in this case would depend on knowing what 
filesystem is used and what parts of the disk the filesystem currently 
has allocated and what is free space. i don't think qemu-img can do this.

you could try just adding -c to the command you listed and qemu-img will 
create a compressed qcow2. that could reduce the size of the resulting 
image significantly. other than that, compressing it further would take 
additional steps.

mike